The present invention relates to a doctor assembly in a paper machine, which is intended to clean a moving surface, such as a roll, felt, or wire. The doctor assembly includes
a doctor blade set against the moving surface
a blade carrier for supporting the doctor blade
a frame
a jointed bearing assembly supporting the blade carrier, and itself supported from the frame component, and parallel to the doctor blade, and
loading devices between the blade carrier and the frame, for rotating the doctor blade in relation to the frame and for pressing the doctor blade against the surface with a selected force;
and in which the jointed bearing assembly between the blade carrier and the frame comprises an operational joint sleeve fixed in one of these components and an operational joint pin fixed in the opposing component, the joint pin being installed to be able to rotate in the joint sleeve.
Here, a paper machine refers broadly to all similar machines, particularly also to board machines. In these machines, a doctor assembly is used to keep the rolls clean. The doctor blade of the doctor assembly cleans fibre residue and water from the surface of the roll and, in case of a web break, guides the web in the desired direction. Doctor assemblies are also used in connection with other moving surfaces, such as felts and wires, in addition to rolls.
A doctor assembly is usually built on a doctor beam, which is set in bearings so that it can be rotated and moved slightly axially, so that it can be moved backwards and forwards with the aid of an oscillating device. The rotatable doctor beam may also have two or more doctors attached to it, each with its own adjustable blade holder. If the doctor beam can be turned, it is used to set the doctor blade in either a maintenance or an operating position. An adjustment device forming part of the doctor assembly is then used to set each doctor blade against the surface with a selected pressure. The doctor assembly includes a holder frame, a jointed bearing assembly, and loading devices, which are generally placed on both sides of the cross-section of the joint.
The doctor blade, blade holder, and holder frame extend unbroken over the entire width of the paper machine. Similarly, the frame and the hoses used as loading devices extend unbroken over the entire width of the paper machine. A jointed bearing assembly, on the other hand, is often only implemented at the ends of the holder frame, in which case the deflection of the latter becomes a problem. U.S. Pat. No. 4,906,335 discloses a doctor assembly, in which the blade holder is supported by several joint members set at intervals. Such assemblies are not, however, in use. Due to the construction of the doctor assembly, the replacement of the doctor blade, or maintenance in general has required the doctor assembly to be turned to a special maintenance position, which is implemented by means of a rotating doctor beam construction. Oscillation has also been connected to this doctor beam.
Known doctor assemblies are extremely heavy, because the doctor beam must be made robust, so that it will turn the blade holder sufficiently also in the centre of the beam, despite deflection. Similarly, the holder frame carrying the doctor blade has generally had to be made quite sturdy, to allow for the great distance between the jointed bearing assemblies.
The present invention is intended to create an entirely new kind of doctor assembly, which is considerably lighter and easier to operate than previous doctor assemblies.
A doctor assembly in a paper machine, which is intended to clean a moving surface, such as a roll, a felt or a wire, and which includes a surface against which a doctor blade is set, a blade support for supporting the doctor blade, a frame, a jointed bearing assembly, which supports the doctor blade and is itself supported from the frame, and which is parallel to the doctor blade, and loading devices between the blade support and the frame for turning the doctor blade in relation to the frame and for pressing the doctor blade against the surface with a selected pressure; and in which the jointed bearing assembly between the blade support and the frame consists or a joint sleeve fixed to one of these components and an operational joint pin fixed to the opposing component and the joint pin is installed to rotate in joint sleeve, characterized in that the jointed bearing assembly extends essentially over the entire width of the doctor blade, either continuously or discontinuously. Because the doctor assembly is supported essentially over its entire width, it no longer need be dimensioned on the basis of deflection. A doctor beam is no longer required, as the doctor assembly is attached directly to the doctor frame. The continuous support is preferably implemented by means of a continuous joint, so that the blade holder can be simply pulled along the joint to replace the blade or for maintenance. According to one preferred embodiment, the joint sleeve is set in the bottom of a structure with a U-shaped cross-section. Both the joint and the loading members are then protected against dirtying. According to another preferred embodiment, a heavy doctor beam with its rotating devices is no longer required at all, as the doctor blade with the blade holder can be pulled out along the longitudinal jointed bearing assembly. Other embodiments and advantages of the invention will become apparent in connection with the following examples of embodiments.
In the following the invention is described with reference to the accompanying figures, in which